150W-1000W mastercolor ceramic metal halide lamp series with color temperature about 4000K, for high pressure sodium or quartz metal halide retrofit applications

ABSTRACT

The invention relates to a high-pressure discharge lamp of the ceramic metal halide type of the Philips MasterColor® series having power ranges of about 150W to about 1000W. Such lamps are provided with a discharge vessel which encloses a discharge space. The discharge vessel has a ceramic wall and is closed by a ceramic plug. An electrode which is located inside the discharge space is connected to an electric conductor by way of a leadthrough element. The leadthrough element projects through the ceramic plug with a close fit and is connected thereto in a gas-tight manner by way of a sealing ceramic. The leadthrough element has a first part which is formed by a cermet at the area of the gas-tight connection. In addition, the lamps display one or more and most preferably all of the following properties: a CCT (correlated color temperature) of about 3800 to about 4500K, a CRI (color rendering index) of about 70 to about 95, a MPCD (mean perceptible color difference) of about ±10, and a luminous efficacy up to about 85-95 lumens/watt, a lumen maintenance of &gt;80%, color temperature shift &lt;200K from 100 hours to 8000 hours, and lifetime of about 10,000 hours to about 25,000 hours. The invention also relates to design spaces for the design and construction of high power lamps and methods for construction of such lamps using the design spaces.

FIELD OF THE INVENTION

[0001] The invention relates to a high-pressure discharge lamp which isprovided with a discharge vessel that encloses a discharge space andincludes a ceramic wall, the discharge space accommodating an electrodewhich is connected to an electric current conductor by means of aleadthrough element. The invention also relates to a high intensitydischarge (HID) lamp having a discharge vessel light source, a glassstem, a pair of leads embedded in the glass stem, a glass envelopesurrounding the light source, and a wire frame member with a first endfixed with respect to the stem, an axial portion extending parallel tothe axis of the lamp, and a second end resiliently fitted in the closedend of the glass envelope.

BACKGROUND OF THE INVENTION

[0002] High intensity discharge (HID) lamps are commonly used in largearea lighting applications, due to their high energy efficiency andsuperb long life. The existing HID product range consists of mercuryvapor (MV), high pressure sodium (HPS), and quartz metal halide (MH)lamps. In recent years, ceramic metal halide lamps (for example, PhilipsMasterColor® series) have entered the market place. Compared to theconventional HID lamps, the ceramic metal halide lamps display excellentinitial color consistency, superb stability over life (lumenmaintenance >80%, color temperature shift <200K at 10,000 hrs), highluminous efficacy of >90 lumens/watt and a lifetime of about 20,000hours. These highly desirable characteristics are due to the highstability of the polycrystalline alumina (PCA) envelopes and a specialmixture of salts, which emits a continuous-spectrum light radiationclose to natural light.

[0003] The salt mixture used in Philips MasterColor® series lamps iscomposed of NaI, CaI₂, TlI, and rare-earth halides of DyI₃, HoI₃ andTmI₃. NaI, CaI₂ and TlI are mainly for emitting high intensity lineradiation at various colors, but they also contribute to continuousradiation. The rare-earth halides are for continuous radiationthroughout the visible range, resulting in a high color rendering index(CRI). By adjusting the composition of the salts, color temperatures of3800-4500K, and a CRI of above 85 can be achieved. The existing powerrange of such lamps is from 20W to 150W. The relatively narrow powerrange makes these products only suitable for the applications requiringlow power installations, such as most indoor low-ceiling retail spaces.For large area, higher power applications requiring a lamp power of 200Wto 1000W, the primary available products are MV, HPS and MH lamps.

[0004] One example of a lamp of the kind set forth is known from U.S.Pat. No. 5,424,609. The known lamp has a comparatively low power of 150W at the most at an arc voltage of approximately 90 V. Because theelectrode in such a lamp conducts comparatively small currents duringoperation of the lamp, the dimensions of the electrode may remaincomparatively small so that a comparatively small internal diameter ofthe projecting plug suffices. In the case of a lamp having a rated powerin excess of 150 W, or a substantially lower arc voltage, for example asin the case of large electrode currents, electrodes of larger dimensionsare required. Consequently, the internal plug diameter will be largeraccordingly. It has been found that in such lamps there is an increasedrisk of premature failure, for example due to breaking off of theelectrode or cracking of the plug.

[0005] There is a need in the art for HID lamps of the ceramic metalhalide type with power ranges of about 150W to about 1000W.

SUMMARY OF THE INVENTION

[0006] An object of the invention is to provide HID lamps of the ceramicmetal halide type with power ranges of about 150W to about 1000W. Thenominal lamp voltage, as specified by applicable ANSI standards for HPSand MH varies from 100V to 135 V for 150W to 400W lamps and thenincreases with the rated power to about 260V for 1000W lamps.

[0007] Another object of the invention is to provide ceramic metalhalide lamps of the Philips MasterColor® series that display excellentinitial color consistency, superb stability over life (lumenmaintenance >80%, color temperature shift <200K at 10,000 hrs), highluminous efficacy of >90 lumens/watt, a lifetime of about 20,000 hours,and power ranges of about 150W to about 1000W.

[0008] Another object is to provide a way to mitigate the drawbacks andrisks of failure discussed above.

[0009] These and other objects of the invention are accomplished,according to a first embodiment of the invention in which an entireproduct family of gas discharge lamps with rated power of 150W to 1000Ware provided which may be coupled with ANSI standard series of ballastsdesigned for high pressure sodium or quartz metal halide lamps(pulse-start or switch-start). The lamps of the invention are anextension of Philips MasterColor® series lamps to a power range of 150Wto 1000W, and they are suitable for same-power HPS or MH retrofit.Therefore, they may be used with most existing ballast and fixturesystems.

[0010] In its preferred embodiments, the invention provides ceramicmetal halide lamps having a power range of about 150W to about 1000W,suitable for high pressure sodium and/or quartz metal halide retrofit.

[0011] In another preferred embodiment, such high power lamps asdescribed above will have one or more and most preferably all of thefollowing properties: a CCT (correlated color temperature) of about 3800to about 4500K, a CRI (color rendering index) of about 70 to about 95, aMPCD (mean perceptible color difference) of about ±10, and a luminousefficacy up to about 85-95 lumens/watt.

[0012] In another preferred embodiment, ceramic metal halide lamps areprovided which have been found, regardless of the rated power, to have alumen maintenance of >80%, color temperature shift <200K from 100 to8000 hours, and lifetime of about 10,000 to about 25,000 hours.

[0013] Especially preferred are ceramic metal halide lamps that displayexcellent initial color consistency, superb stability over life (lumenmaintenance >80%, color temperature shift <200K at 10,000 hrs), highluminous efficacy of >90 lumens/watt, a lifetime of about 20,000 hours,and power ranges of about 150W to about 1000W.

[0014] The invention also provides novel design spaces containingparameters for any lamp power between about 150W and 1000W in whichappropriate parameters for the body design of a lamp operable at thedesired power is obtained by selection from parameters in which (i) thearc tube length, diameter and wall thickness limits are correlated toand expressed as functions of lamp power, and/or color temperature,and/or lamp voltage, and (ii) the electrode feedthrough structure usedto conduct electrical currents with minimized thermal stress on the arctube are correlated to and expressed as a function of lamp current. Theinvention also provides methods for producing ceramic metal halide lampshaving predetermined properties through use of the design spaces of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above aspects and further aspects of the lamps in accordancewith the invention will be described in detail hereinafter withreference to the drawing in which:

[0016]FIG. 1 is a graph illustrating a range of upper and lower limitsfor the dimensions of the arc tube inner length in a preferredembodiment of the invention;

[0017]FIG. 2 is a graph illustrating a range of upper and lower limitsfor the dimensions of the arc tube inner diameter in a preferredembodiment of the invention;

[0018]FIG. 3 is a graph illustrating a design space of the limits ofaspect ratio in a preferred embodiment of the invention;

[0019]FIG. 4 is a graph illustrating a design space of wall loadingversus power in a preferred embodiment of the invention;

[0020]FIG. 5 is a graph illustrating a range of upper and lower limitsfor the dimensions of the arc tube wall thickness versus the lamp powerin a preferred embodiment of the invention;

[0021]FIG. 6 is a graph illustrating a range of upper and lower limitsfor electrode rod diameter versus power in a preferred embodiment of theinvention;

[0022]FIG. 7 is a graph illustrating a range of upper and lower limitsfor electrode rod lengths versus power in a preferred embodiment of theinvention;

[0023]FIG. 8 is a schematic of a lamp according to a preferredembodiment of the invention;

[0024]FIG. 9 is a sectional view of a ceramic arc tube of FIG. 8according to a preferred form of the invention;

[0025]FIG. 10 is a sectional view of a three-part electrode feedthroughof FIG. 8 according to a preferred form of the invention; and

[0026]FIG. 11 is a graph of lumen maintenance of 150W and 200W lampsaccording to a preferred form of the invention.

[0027] The invention will be better understood with reference to thedetails of specific embodiments that follow:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Referring to FIG. 8, a ceramic metal halide discharge lamp 1comprises a glass outer envelope 10, a glass stem 11 having a pair ofconductive frame wires 12, 13 embedded therein, a metal base 14, and acenter contact 16 which is insulated from the base 14. The stem leads12, 13 are connected to the base 14 and center contact 16, respectively,and not only support the arc tube 20 but supply current to theelectrodes 30, 40 via frame wire member 17 and stem lead member 13. Agetter 18 is fixed to the frame wire member 17. Niobium connectors 19provide an electrical connection for the arc tube electrode feedthroughs30 and 40. Beyond this the frame member 17 is provided with an endportion 9 that contacts a dimple 8 formed in the upper axial end of theglass envelope 10.

[0029]FIG. 9 shows a preferred embodiment of the arc tube 20 having afour-part feedthrough in cross-section. The central barrel 22 is formedas a ceramic tube having disc-like end walls 24, 25 with centralapertures which receive end plugs 26, 27. The end plugs are also formedas ceramic tubes, and receive electrodes 30, 40 therethrough. Theelectrodes 30, 40 each have a lead-in 32, 42 of niobium which is sealedwith a frit 33, 43 which hermetically seals the electrode assembly intothe PCA arc tube, a central portion 34, 44 of molybdenum/aluminumcermet, a molybdenum rod portion 35, 45 and a tungsten rod 36, 46 havinga winding 37, 47 of tungsten. The barrel 22 and end walls 24, 25 enclosea discharge space 21 containing an ionizable filling of an inert gas, ametal halide, preferably a mixture of metal halides, and mercury.

[0030]FIG. 10 shows a second preferred embodiment of the arc tube 20having a three-part feedthrough in cross-section. The electrodes 30, 40(only 30 is illustrated) each have a lead-in 32, 42 of niobium which issealed with a frit 33, 43, a central portion 34, 44 of molybdenum orcermet, and a tungsten rod 36, 46 having a winding 37, 47 of tungsten.

[0031] As used herein, “ceramic” means a refractory material such as amonocrystalline metal oxide (e.g. sapphire), polycrystalline metal oxide(e.g. polycrystalline densely sintered aluminum oxide and yttriumoxide), and polycrystalline non-oxide material (e.g. aluminum nitride).Such materials allow for wall temperatures of 1500-1600K and resistchemical attacks by halides and Na. For purposes of the presentinvention, polycrystalline aluminum oxide (PCA) has been found to bemost suitable.

[0032]FIG. 8 also shows a ceramic metal halide arc tube 20 having aconductive antenna coil 50 extending along the length of barrel 22. Asdescribed further hereinbelow, the antenna coil 50 reduces the breakdownvoltage at which the fill gas ionizes by a capacitive coupling betweenthe coil and the adjacent lead-in in the plug. When an AC voltage isapplied across the electrodes, the antenna stimulates UV emission in thePCA, which in turn causes primary electrons to be emitted by theelectrode. The presence of these primary electrons hastens ignition of adischarge in the fill gas.

[0033] Thus to summarize, there is provided high wattage discharge lampswhich comprise a ceramic discharge vessel which encloses a dischargespace and is provided with preferably a cylindrical-shaped ceramic,preferably a sintered translucent polycrystalline alumina arc tube withelectrodes, preferably tungsten-molybdenum-cermet-niobium electrodes,attached on either side by gas-tight seals. Metallic mercury, a noblegas or a mixture of noble gases and radioactive ⁸⁵Kr, and a salt mixturecomposed of sodium iodide, calcium iodide, thallium iodide and severalrare earth iodides are contained in the arc tube. The arc tube isprotected from explosion by a tungsten or molybdenum coil, which alsoserves as antenna for starting. The entire arc tube and its supportingstructure are enclosed in a standard-size lead-free hard glass bulb,with other components such as a getter (18 in FIG. 8) or an UV enhancer(not shown) attached as necessary.

[0034] In preferred embodiments of the invention, the following designparameters have been found to mitigate and in most cases eliminate theeffects of higher thermal stress associated with the higher lamp powers.We have found the parameters to be especially suitable for theproduction of lamp products of 150W to 400W of power and 100V of lampvoltage, and with modifications in some of the design parameters, lampswith 135V-260V voltage and/or higher powers (up to 1000W) may also bedesigned. These design parameters are:

[0035] (i) the general aspect ratio, i.e. the ratio of the inner length(IL) to the inner diameter (ID) of the PCA arc tube body is higher thanthat of low power-range MasterColor® lamps.

[0036] (ii) general design spaces for any lamp power between 150W and1000W, in terms of arc tube length, diameter and wall thickness limits,are expressed as functions of lamp power, color temperature, and lampvoltage and the upper and lower limits of such parameters are determinedfor the selected lamp powers and a method is provided for selectingparameters from the design space to provide a lamp with previouslyselected characteristics.

[0037] (iii) a unique laser-welded Tungsten-cermet-Niobium orTungsten-molybdenum-cermet-Niobium electrode feedthrough structure isused to conduct large electrical currents with minimized thermal stresson the PCA.

[0038] (iv) the design parameter limits of such feedthroughs are givenas the function of lamp current.

[0039] (v) for reducing the risk of non-passive failure, a molybdenumcoil wrapped around the arc tube and around the extended plugs is usedas disclosed in our U.S. patent application Ser. No. ______ (DisclosureNo. 701713 filed of even date herewith as a divisional application ofthis application for “Coil Antenna/Protection For Ceramic Metal HalideLamps”.

[0040] (vi) the salt composition is adjusted, to the desired colortemperatures, for the geometry and varying lamp voltages of the highpower MasterColor® lamps.

[0041] (vii) the starting characteristics of the lamps are accomplishedby using a mixture of Xenon, Argon, Krypton and ⁸⁵Kr gases.

[0042] Referring to FIGS. 1 to 7 and 11, the above design parameters maybe categorized as including one or more of the following:

[0043] (1) Design space limits for arc tube geometry;

[0044] (2) Electrode feedthrough construction and design limits;

[0045] (3) Composition range of iodide salts for achieving desiredphotometric properties (CCT=3800-4500K, CRI=85-95, MPCD=±10, luminousefficacy of 85-95 lumens/watt); and

[0046] (4) Buffer gas composition and pressure range.

[0047] An especially important aspect of the invention lies in thediscovery of the parameter limits within which the whole product familyhaving a power of 150W to 1000W, regardless of the specific rated power,has a lumen maintenance of >80% at 8000 hours (see FIG. 11 for anexample); color temperature shift <200K from 100 hours to 8000 hours;and a lifetime in a range of 10,000 hours to 25,000 hours.

[0048] Design Space for Arc Tube Geometry

[0049] The arc tube geometry is defined by a set of parameters bestillustrated in FIGS. 1 to 5 and FIG. 9 which also illustrates majorparameters used. As seen in FIGS. 1 and 9, the arc tube body innerlength (IL) is determined by lamp power. The upper and lower limit of ILfor any given lamp power between 150W and 400W can be found in FIG. 1.

[0050] The arc tube body inner diameter (ID) is also a function of lamppower. The upper and lower limits of the ID for any given lamp powerfrom 150W to 400W are shown in FIG. 2.

[0051] One of the common characteristics of this higher wattageMasterColor® lamp family is that the aspect ratio of the arc tube bodyis higher than that of the lower wattage (30-150W) Philips MasterColor®lamps, which is about 1.0. For any given lamp power for the lamps of thepresent invention, the aspect ratio (IL/ID) falls into a range of3.3-6.2. The geometric design space is shown in an IL-ID plot in FIG. 3.The shaded space shown in FIG. 3 is the general design space which doesnot specify lamp power.

[0052] How each design is compared with others of different rated powersis measured by “wall loading”. Wall loading is defined as the ratio ofpower and the inner surface area of arc tube body, in a unit of W/cm².In FIG. 4, the upper line is the wall loading value as if the IL and IDare both at their lower limits for the power, therefore the innersurface area is the minimum and wall loading is at maximum. The lowerline is the wall loading level as if both IL and ID are at upper limits,making the surface area the maximum and wall loading minimum. Any otherdesigns should have a wall loading range between 23-35W/cm², asindicated by the individual points inside the shaded area. Across thepower range of 150W to 400W, the wall loading level remains fairlyconstant.

[0053] Generally, arc tubes for higher lamp power require a thickerwall, in accordance with the larger volume. The limits of the wallthickness are specified in FIG. 5.

[0054] Electrode Feedthrough Construction and Design Parameters

[0055] Electrodes for conducting current and acting alternatively ascathode and anode for an arc discharge are constructed specifically forthe ceramic arc tubes. FIGS. 9 and 10 give the details of the componentsand their relative positions in the arc tube and show the preferredembodiments of the arc tube 20 having a four-part and a three-partfeedthrough, respectively, in which electrodes 30, 40 each have alead-in 32, 42 of niobium which is sealed with a frit 33, 43, a centralportion 34, 44 of molybdenum/aluminum cermet, a molybdenum rod portion35, 45 and a tungsten tip (rod) 36, 46 having a winding 37, 47 oftungsten and/or in which electrodes 30, 40 each have a lead-in 32, 42 ofniobium which is sealed with a frit 33, 43, a central portion 34, 44 ofmolybdenum/aluminum cermet, and a tungsten tip (rod) 36, 46 having awinding 37, 47 of tungsten. Preferably, each joint connecting twofeedthrough components is welded by a laser welder. Although thethree-part feedthrough structure is similar to those used in the lowerwattage Philips MasterColor® lamps, the preferred design parameters forconstructing the feedthroughs for larger current are given here.

[0056] The primary design parameters for feedthroughs include electroderod diameter and length as illustrated in FIGS. 6 and 7 which indicatethe limits for rod diameter and rod length, versus lamp current.

[0057] Preferably additional parameters are present for the preferredembodiments of the feedthrough construction and include (1) the tipextension of the electrode is in the range of 0.2-1.0 mm, (2) thetip-to-bottom (ttb) distance, i.e. the length of electrode indise thetube arc body, is in a range of 1 mm to 4 mm and generally increaseswith power, (3) cermet should contain no less then about 35 wt. % Mo,with a preferred Mo content of no less than about 55 wt. % with theremainder being Al₂O₃, and (4) the frit (also known as sealing ceramic)flow should completely cover the Nb rod.

[0058] Thus we have found that the following approximations of PCA arctube and feedthrough characteristics define design spaces in which thedesired lamp power may be selected from the parameters and vice versa:TABLE I IL/ID Wall Wall Rod Rod Power IL ID Aspect Loading ThicknessDiameter Length W mm mm Ratio, mm W/cm² mm mm mm 150 26-32 5-7 3.3-6.220-35 0.8-1.1 0.4-0.6 3-6  200 27-32 6.5-7.5 3.3-6.2 25-30 0.85-1.20.4-0.6 4-8  250 28-34 7.5-8.5 3.3-6.2 25-35 0.9-1.3 0.7-1.0 6-10 30030-36 8-9 3.3-6.2 25-37 0.92-1.4 0.7-1.0 6-10 350 33-40 8.5-10  3.3-6.224-40 0.98-1.48 0.7-1.1 6-11 400 36-45 8.5-11  3.3-6.2 22-40 1.0-1.50.7-1.1 6-11

[0059] Preferably also (1) the tip extension of the electrode is in therange of 0.2-1.0 mm, (2) the tip-to-bottom (ttb) distance is in a rangeof 1 mm to 4 mm and generally increase with power, (3) the cermetcontains no less then about 35 wt. % Mo, with a preferred Mo content ofno less than about 55 wt. % with the remainder being Al₂O₃, and (4) thefrit (also known as sealing ceramic) flow completely covers the Nb rod.

[0060] Composition of Metal Halide Salt Mixture

[0061] The salt mixture is specially designed for the power range andarc tube geometry used for this product family. The following tablegives the nominal composition of the salt mixture wherein the totalcomposition is 100%: TABLE II Salt NaI TlI CaI₂ DyI₃ HoI₃ TmI₃ Wt. %6-25 5-6 34-37 11-18 11-18 11-18

[0062] Buffer Gas Composition and Pressure Range

[0063] The filling of the discharge vessel includes 1-5 mg Hg. Themercury content is similar to that of Philips' Alto® Plus lamps, i.e.about <5 mg and the lamps of the invention have passed the TCLP test andthus are environmentally friendly. In addition, the lamps also contain10-50 mg metal halides in a ratio of 6-25 wt % NaI, 5-6 wt % TlI, 34-37wt % CaI₂, 11-18 wt % DyI₃, 11-18 wt % HoI₃, and 11-18 wt % TmI₃. Thearc tube is also filled with a mixture of noble gases for assisting lampignition. The composition of the gas is a minimum of about 99.99% ofXenon and a trace amount of ⁸⁵Kr radioactive gas but may use a mixtureof Ar, Kr and Xe instead of pure Xe as a possible alternative. Purexenon is preferred since the lamp efficacy has been indicated to behigher when compared to lamps with Ar. Additionally, the breakdownvoltage of lamps utilizing xenon is higher than that of lamps with Ar,and the wall temperature of lamps is lower than that of lamps with Ar.The room temperature fill pressure of this product family is preferablyin a range of about 50 torr to about 150 torr.

[0064] Molybdenum Coil

[0065] As discussed above, for reducing the risk of non-passive failure,a molybdenum coil wrapped around the arc tube and around the extendedplugs is used as disclosed in our U.S. patent application Ser. No.______ (Disclosure No. 701713) filed of even date herewith as adivisional application of this application for “Coil Antenna/ProtectionFor Ceramic Metal Halide Lamps”.

[0066] This application discloses a Mo coil antenna wrapped around a PCAarc tube and around at least a portion of the extended plugs. The coilantenna serves as an antenna for starting or ignition, provides goodcapacitive coupling for ignition, has no adverse effect on the efficacyor lifetime properties of the lamps, and also provides mechanicalcontainment of particles in the event of arc tube rupture.

[0067] The product family will have a wide range of usage in both indoorand outdoor lighting applications. The primary indoor applicationsinclude constantly occupied large-area warehouse or retail buildingsrequiring high color rendering index, high visibility and lowlamp-to-lamp color variation. Outdoor applications include city streetlighting, building and structure illumination and highway lighting.

[0068] It will be understood that the invention may be embodied in otherspecific forms without departing from the spirit and scope or essentialcharacteristics thereof, the present disclosed examples being onlypreferred embodiments thereof.

We claim:
 1. A discharge lamp comprising a ceramic discharge vesselenclosing a discharge space, said discharge vessel including within saiddischarge space an ionizable material comprising a metal halide, a firstand second discharge electrode feedthrough means, and a first and secondcurrent conductor connected to said first and second discharge electrodefeedthrough means, respectively; said lamp having a power range of about150W to about 1000W and exhibiting one or more of a characteristicselected from the group consisting of a CCT (correlated colortemperature) of about 3800 to about 4500K, a CRI (color rendering index)of about 70 to about 95, a MPCD (mean perceptible color difference) ofabout ±10, and a luminous efficacy up to about 85-95 lumens/watt.
 2. Alamp as claimed in claim 1 retrofit with ballasts and lighting fixturesdesigned for high pressure sodium or quartz metal halide lamps.
 3. Adischarge lamp having a power range of about 150W to about 1000W andcomprising a ceramic discharge vessel enclosing a discharge space, saiddischarge vessel including within said discharge space an ionizablematerial comprising a metal halide, a first and second dischargeelectrode feedthrough means, and a first and second current conductorconnected to said first and second discharge electrode feedthroughmeans, respectively; wherein the ceramic discharge vessel includes anarc tube comprising: a cylindrical barrel having a central axis and apair of opposed end walls, a pair of ceramic end plugs extending fromrespective end walls along said axis, a pair of lead-ins extendingthrough respective end plugs, said lead-ins being connected torespective electrodes which are spaced apart in said central barrel,wherein the electrode feedthrough means each have a lead-in of niobiumwhich is hermetically sealed into the arc tube, a central portion ofmolybdenum/aluminum cermet, a molybdenum rod portion and a tungsten rodhaving a winding of tungsten.
 4. A lamp as claimed in claim 3, whereinthe arc tube has a molybdenum coil attached to its surface.
 5. A lamp asclaimed in claim 4, wherein the discharge space contains an ionizablefilling of an inert gas, a mixture of metal halide, and mercury.
 6. Alamp as claimed in claim 5 wherein, said discharge vessel has a ceramicwall and is closed by a ceramic plug, said electrode feedthrough meansincluding at least one tungsten electrode which is connected to aniobium electric current conductor by means of a leadthrough elementwhich projects into the ceramic plug with a tight fit, is connectedthereto in a gas-tight manner by means of a sealing ceramic and has apart formed from aluminum oxide and molybdenum which forms a cermet atthe area of the gas-tight connection.
 7. A lamp as claimed in claim 5,wherein, said discharge vessel has a ceramic wall and is closed by aceramic plug, said electrode feedthrough means including at least onetungsten electrode which is connected to a niobium electric currentconductor by means of a leadthrough element which projects into theceramic plug with a tight fit, is connected thereto in a gas-tightmanner by means of a sealing ceramic and has a first part formed fromaluminum oxide and molybdenum which forms a cermet at the area of thegas-tight connection and a second part which is a metal part and extendsfrom the cermet in the direction of the electrode.
 8. A lamp as claimedin claim 7, wherein the metal part is a molybdenum rod.
 9. A lamp asclaimed in claim 5, wherein the arc tube has an aspect ratio (IL/ID) inthe range of about 3.3 to about 6.2.
 10. A lamp as claimed in claims 6and 7, wherein the electrode has a tip extension in the range of about0.2 to about 1.0 mm; the cermet contains at least about 35 wt. % Mo withthe remainder being Al₂O₃, and the sealing ceramic flow completelycovers the Nb connector.
 11. A lamp as claimed in claim 10, wherein thearc tube and the electrode feedthrough means have the followingcharacteristics for a given lamp power: IL/ID Wall Wall Rod Rod Power ILID Aspect Loading Thickness Diameter Length W mm mm Ratio, mm W/cm² mmmm mm 150 26-32 5-7 3.3-6.2 20-35 0.8-1.1 0.4-0.6 3-6  200 27-32 6.5-7.53.3-6.2 25-30 0.85-1.2 0.4-0.6 4-8  250 28-34 7.5-8.5 3.3-6.2 25-350.9-1.3 0.7-1.0 6-10 300 30-36 8-9 3.3-6.2 25-37 0.92-1.4 0.7-1.0 6-10350 33-40 8.5-10  3.3-6.2 24-40 0.98-1.48 0.7-1.1 6-11 400 36-45 8.5-11 3.3-6.2 22-40 1.0-1.5 0.7-1.1 6-11


12. A lamp as claimed in claim 11, wherein said metal halide mixturecomprises the following salts of 6-25 wt % NaI, 5-6 wt % TlI, 34-37 wt %CaI₂, 11-18 wt % DyI₃, 11-18 wt % HoI₃, and 11-18 wt % TmI₃.
 13. A lampas claimed in claim 12, wherein the ionizable filling is a mixture ofabout 99.99% of Xenon and a trace amount of ⁸⁵Kr radioactive gas.
 14. Alamp as claimed in claim 12, wherein the ionizable filling is a mixtureof Argon and/or Krypton, Xenon, and a trace amount of ⁸⁵Kr radioactivegas.
 15. A lamp as claimed in claim 12, wherein the ionizable filling isXenon. and/or Krypton.
 16. A lamp as claimed in claims 1, 5, and 13,having a power range of about 150W to about 1000W and nominal voltage of100V to 260V, and one or more of the following characteristics: a lumenmaintenance of >80%, a color temperature shift <200K from 100 to 10,000hours, and lifetime of about 10,000 to about 25,000 hours.
 17. A designspace of parameters for the design and construction of a discharge lamphaving a power range of about 150W to about 1000W and comprising aceramic discharge vessel enclosing a discharge space, said dischargevessel including within said discharge space an ionizable materialcomprising a metal halide mixture, a first and second dischargeelectrode feedthrough means, and a first and second current conductorconnected to said first and second discharge electrode feedthroughmeans, respectively; said design space including at least one of thefollowing parameters: (i) the arc tube length, diameter and wallthickness limits of said discharge lamp correlated to and expressed asfunctions of lamp power, and/or color temperature, and/or lamp voltage;and (ii) the electrode feedthrough structure limits used to conductelectrical currents with minimized thermal stress on the arc tubecorrelated to and expressed as a function of lamp current.
 18. A designspace as claimed in claim 17, wherein said parameters also include: (i)a general aspect ratio of the inner length (IL) to the inner diameter(ID) of the arc tube body is higher than that of ceramic metal halidelamps having a power of less than about 150W; (ii) the upper and lowerlimits of electrode rod diameter correlated to and expressed as afunction of lamp current; and (iii) a composition range of the saltscorrelated to color temperature and lamp voltage.
 19. A design space asclaimed in claim 18, wherein said design parameters include thefollowing characteristics for the design of an arc tube and electrodefeedthrough means for a given lamp power: IL/ID Wall Wall Rod Rod PowerIL ID Aspect Loading Thickness Diameter Length W mm mm Ratio, mm W/cm²mm mm mm 150 26-32 5-7 3.3-6.2 20-35 0.8-1.1 0.4-0.6 3-6  200 27-326.5-7.5 3.3-6.2 25-30 0.85-1.2 0.4-0.6 4-8  250 28-34 7.5-8.5 3.3-6.225-35 0.9-1.3 0.7-1.0 6-10 300 30-36 8-9 3.3-6.2 25-37 0.92-1.4 0.7-1.06-10 350 33-40 8.5-10  3.3-6.2 24-40 0.98-1.48 0.7-1.1 6-11 400 36-458.5-11  3.3-6.2 22-40 1.0-1.5 0.7-1.1 6-11


20. A method for the design and construction of a discharge lamp havinga power range of about 150W to about 1000W and comprising a ceramicdischarge vessel enclosing a discharge space, said discharge vesselincluding within said discharge space an ionizable material comprising ametal halide mixture, a first and second discharge electrode feedthroughmeans, and a first and second current conductor connected to said firstand second discharge electrode feedthrough means, respectively; whichmethod comprises the steps of determining the dimensions of the arc tubeof the discharge vessel and the electrode feedthrough means structureusing a design space of claim
 17. 21. A method for the design andconstruction of a discharge lamp having a power range of about 150W toabout 1000W and comprising a ceramic discharge vessel enclosing adischarge space, said discharge vessel including within said dischargespace an ionizable material comprising a metal halide mixture, a firstand second discharge electrode feedthrough means, and a first and secondcurrent conductor connected to said first and second discharge electrodefeedthrough means, respectively; which method comprises the steps ofdetermining the dimensions of the arc tube of the discharge vessel andthe electrode feedthrough means structure using a design space of claim18.
 22. A method for the design and construction of a discharge lamphaving a power range of about 150W to about 1000W and comprising aceramic discharge vessel enclosing a discharge space, said dischargevessel including within said discharge space an ionizable materialcomprising a metal halide, a first and second discharge electrodefeedthrough means, and a first and second current conductor connected tosaid first and second discharge electrode feedthrough means,respectively; which method comprises the steps of determining thedimensions of the arc tube of the discharge vessel and the electrodefeedthrough means structure using a design space of claim
 19. 23. Amethod as claimed in claim 22, including the further design parameterthat the metal halide comprises the following salts of 6-25 wt % NaI,5-6 wt % TlI, 34-37 wt % CaI₂, 11-18 wt % DyI₃, 11-18 wt % HoI₃, and11-18 wt % TmI₃.
 24. A method as claimed in claim 23, including thefurther design parameter that the ionizable filling is a mixture ofabout 99.99% of Xenon and a trace amount of ⁸⁵Kr radioactive gas.
 25. Amethod as claimed in claim 24, including the further design parameterthat the discharge vessel has a ceramic wall and is closed by a ceramicplug, said electrode feedthrough means including at least one tungstenelectrode which is connected to a niobium electric current conductor bymeans of a leadthrough element which projects into the ceramic plug witha tight fit, is connected thereto in a gas-tight manner by means of asealing ceramic and has a part formed from aluminum oxide and molybdenumwhich forms a cermet at the area of the gas-tight connection.
 26. Amethod as claimed in claim 24, including the further design parameterthat the discharge vessel has a ceramic wall and is closed by a ceramicplug, said electrode feedthrough means including at least one tungstenelectrode which is connected to a niobium electric current conductor bymeans of a leadthrough element which projects into the ceramic plug witha tight fit, is connected thereto in a gas-tight manner by means of asealing ceramic and has a first part formed from aluminum oxide andmolybdenum which forms a cermet at the area of the gas-tight connectionand a second part which is a metal part and extends from the cermet inthe direction of the electrode.
 27. A method as claimed in claim 26,wherein the metal part is a molybdenum rod.
 28. A method as claimed inclaims 25 and 26, wherein the electrode has a tip extension in the rangeof about 0.2 to about 1.0 mm; the cermet contains at least about 35 wt.% Mo with the remainder being Al₂O₃, and the sealing ceramic flowcompletely covers the Nb connector.
 29. A method as claimed in claim 20wherein the lamp produced has a power range of about 150W to about 1000Wand nominal voltage of 100V to 260V, and one or more of the followingcharacteristics: a lumen maintenance of >80%, a color temperature shift<200K from 100 to 8,000 hours, and lifetime of about 10,000 to about25,000 hours.